1. Technical Field
The present disclosure relates generally to an apparatus and method for a manually operated plunger bar for creating holes. In particular, the plunger bar is designed to attenuate transmitted shock forces between the tool and the operator.
2. Description of Related Art
Plunger bars are used to create holes in soil, concrete, etc. The most common users are gas utility personnel which use the devices to make holes in the ground or between cracks in pavement in order to insert a gas detection sniffer and locate possible gas leaks. The prior art plunger bar is a manually operated device, designed to be portable and stowable on a service truck for use at remote locations.
FIG. 1 shows an assembly of the prior art plunger bar 10. The plunger bar is generally used in a substantially vertical orientation. The plunger bar comprises a handle 26 which has a piston 18 and a barrel 16. The barrel 16 is free to slide down the length of the piston 18 and the barrel's motion is halted upon impact with a flange 20 located at the lower end of the piston 18. The barrel 16 envelopes the piston 18 when the barrel is in the down position. The barrel has a hammer 14 attached at its lower end which is consequently also the point of impact with the flange 20 when the plunger bar 10 is in use. The hammer supplies extra weight to the barrel 16 hence increasing the impact load when impacting the flange 20. On the end of piston 18 opposite the barrel 16, there is a probe 30 which comprises a solid rod 22 fixedly attached to the piston 18 and a removable conical tip 28 at the free end. The tip 28 can therefore be replaced if damaged. The removable tip 28 is generally sized 3/16 inches to 1/4 inches larger than the diameter of the rod 22. This is to reduce the friction on the rod when a portion of the rod is buried during use.
The barrel 16 is raised by an operator to a maximum height as defined by the hammer 14 and a flange 12 on the end of the piston 18 opposite the probe 30. At this point the operator accelerates the barrel 16 by releasing it or driving it downward. The downward velocity of the barrel 16 and hammer 14 increases until impact. The combined mass of the barrel 16 and hammer 14 multiplied by the velocity at impact gives the momentum imparted to the flange 20 thereby forcing the probe 30 with the removable conical tip 28 into the ground. The penetration of the rod into the ground is achieved when the impulsive impact force of the barrel 16 and hammer 14 overcome the soil resistance force. After the impact, the hammer 14 and barrel 16 recoils and loses contact with flange 20, and the probe 30 is driven further into the ground.
An operator is responsible for securing the plunger bar 10 upright during its operation. The operator also provides the necessary energy to the barrel 16 by lifting it and forcing it downward. In order to be able to complete both activities, it is necessary for the operator to hold the barrel 16 through the impact. This presents some difficulty when harder soils, rocks, concrete, etc. are encountered. Softer soils damp out harmful vibrations, but when a very high resistance is encountered the vibrations due to impacts are no longer damped and are transferred through the plunger bar 10 into the operator. In very high resistance media, the probe 30 cannot penetrate, and this reduces the impact time to a minimum forcing the operator to experience the maximum impact force.
The impact forces transferred to the operator can cause injury. Immediate damage is possible due to stresses imparted to the arms and wrists of the operator. Also fatigue injuries are common over time or with repetitive use of the plunger bar 10. Therefore, a need exists for a plunger bar that reduces stresses imparted to operators by reducing the impact loads during operation.